Method of crosslinking cellulosic fibres

ABSTRACT

Crosslinking of cellulose fibres to obtain good finishing effects while retaining a high degree of abrasion resistance is accomplished by a process which comprises treating cellulose fibres with a solution containing (1) as crosslinking agent 0.5 1.5, preferably 0.6 - 1.0 mols per litre, of a mixture of an aldehyde having a molecular weight not higher than 60 and a nitrogeneous component having a molecular weight not higher than 250, which nitrogeneous compound has at least two N-CH2OH groups adjacent to carbonyl groups, the molar ratio between the aldehyde and the nitrogeneous compound ranging between 12:1 and 2:1, preferably between 6:1 and 0:1, (2) a catalytically effective amount of a mixture consisting of (a) a potentially acidic inorganic salt of magnesium or zinc, preferably magnesium chloride, and (b) a salt of fluorine-containing acid selected from the group consisting of alkali metal, alkaline earth metal and zinc fluoborates and silicofluorides, the molar ratio of the potentially acidic salt to the fluorine-containing salt ranging between 5:1 and 15:1, and the molar concentration of the crosslinking agent in the bath ranging from 1:4 to 1:15, and (3) as an abrasion resistance improving additive from 0:3 to 3 mols of a neutral alkali metal salt of an inorganic monobasic acid.

United States Patent [1 1 Lauehenauer [451 Apr. 30, 1974 4] METHOD OFCROSSLINKING CELLULOSIC FIBRES 8/18, 8/l15.6, 8/115.7, 8/ll6.4, 8/129,

8/181, 8/182, 8/186, 8/187, 8/192, 8/194, 8/196, 8/DIG. 4, 8/9, 8/12,8/17, 8/21, 38/144, 117/9331, 117/1394, 260/29.4 R. Int. C1.D06m 13/12,D06m 15/56, D06m 15/58 Field of Search 8/11613, 116.4, 116.2, 8/181,182, 186, 187, 192; 38/144 [56] References Cited UNITED STATES PATENTS2,541,457 2/1951 Beer 3/1164 2,602,018 7/1952 Beer 8/1 16.3

3,443,987 5/1969 Ferrante 8/1 16.4

2,826,514 3/1958 Schroeder 8/1 16.4 3,173,751 3/1965, Daul et a1. 8/116.4 3,181,927 5/1965 Roth et a]. 8/1 16.3 3,220,869 ll/l965 Ruemens eta1. 8/1 16.3 3,369,858 2/1968 Lourigan et a1. 8/1 1613 3,441,366 4/1969Pierce et a1 8/1 16.3 3,617,199 ll/l97l Russell 8/1164 3,622,261 ll/l97lCotton et al... 3/1 16.4 3,656,885 4/1972 Gagliardi 8/1 16.3 3,674,4187/1972 Lyons et a1. 8/116.3 3,676,053 7/1972 Miyake et a1. 8/l l6.4

FOREIGN PATENTS OR APPLICATIONS 4/1965 Great Britain 8/1 16.3

1,120,965 7/1968 Great Britain 8/116.4

Primary ExaminerGeorge F. Lesmes Assistant Examiner 1. Cannon Attorney,Agent, or Firml-Iowson and Howson [57] ABSTRACT Crosslinking ofcellulose fibres to obtain good finishing effects while retaining a highdegree of abrasion resistance is accomplished by a process whichcomprises treating cellulose fibres with a solution containing (1) ascrosslinking agent 0.5 1.5, preferably 0.6 1.0 mols per litre, of amixture of an aldehyde having a molecular weight not higher than 60 anda nitrogeneous component having a molecular weight not .higher than 250,which nitrogeneous compound has at least two NCH OH groups adjacent tocarbonyl groups, the molar ratio between the aldehyde and thenitrogeneous compound: ranging between 12:1 and 2:1, preferably between6:1 and 0:1, (2) a catalytically effective amount of a mixtureconsisting of (a) a po-' I tentially acidic inorganic salt of magnesiumor zinc,

preferably magnesium chloride, and (b) a salt of fluorine-containingacid selected from the group consisting of alkali metal, alkaline earthmetal and zinc fluoborates and silicofluorides, the molar ratio of thepotentially acidic salt to the fluorine-containing salt ranging between5:1 and 15:1, and the molar concen tration of the crosslinking'agent inthe bath ranging from 1:4 to 1:15, and (3) as an abrasion resistanceimproving additive from 0:3 to 3 mols of a neutral alkali metal salt ofan inorganic monobasic acid.

14 Claims, N0 Drawings METHOD OF CROSSLINKING CELLULOSIC FIBRES.

Cellulosic fibres are known to retain creases when subjected totreatments such as actual wear or laundering, which cause fibres in theform of textile sheet material to be flexed, folded or creased.Thisdeficiency may be overcome by increasing the intermolecular cohesionof cellulosic fibres, i.e., by forming additional bonds between adjacentcellulose chains. Such additional intermolecular bonds have to beintroduced in such a number that the crosslinked fibre is no longersoluble in cellulose solvents such as cuprammonium. By crosslinking,effects commonly known as dimensional stability, crease-proofing, washand wear and durable press properties may be achieved on textile sheetmaterial at least partly consisting of cellulose fibres, in particularof cotton. A large number of chemically different crosslinking agents,crosslinking catalysts and crosslinking procedures have been proposedover the last 40 years and many of these formulations are or have beenwidely used. Irrespective of their chemical nature, these crosslinkingformulations are known to produce undesirable side-effects, inparticular a reduction of tensile, tear and abrasion strengths of thecellulosic material. These strength losses unfortunately grow withdesirable effects such as creaserecovery angles and wash-and-wearratings. Even small deviations from optimum processing conditions maylead not only to erratic and unpredictable results, but also to anincrease of undesirable side-effects.

To obtain good effects, high concentrations of relatively expensivecrosslinking agents have to be used.

High bath concentrations may cause the formation of surface deposits dueto migration of these agents from the interior of fibres to the surfaceduring drying. Since such surface deposits may seriously affectdesirable properties and the handle of the textile material treated,they have to be removed by afterwashing followed by drying, whichfurther increases the cost of such processes. To vary finishing effectswith conventional crosslinking formulations to meet requirementsdiffering as to the degree of crosslinking, the ratio between dry andwet crease recovery, chlorine retention or costs, one had in many casesto apply chemically different agents. The actual crosslinking treatment,practically always carried out by subjecting the textile materialcontaining the crosslinking agent and the crosslinking catalyst to aheat treatment (curing) after drying, required a carefully selectedbalance between curing time and curing temperature if excessivetendering of the cellulosic fibres was to be avoided, the duration ofthe heat treatment having to be increased when the curing temperaturewas lowered and vice versa. There was, however, an upper limit of about180C. to the curing temperature due to the adverse effect such hightemperatures might have on dye-stuffs, fluorescent brighteners and otherfinishing agents present. Even at this upper limitof the'temp'eraturerange, curing times would not be much below about 30 seconds. There wasalso a lower limit to the curing temperature, i.e., a thresholdtemperature below which crosslinking would take place insufficiently ornot at all even if curing times were increasedto for instance 5 minutes.or more. This lower threshold temperature for most know crosslinkingformulations was in the range of 130 to 150C. depending on the chemicalnature of the agents involved. It thus was impossible to adjust within awide range a given conventional crosslinking formulation to curingconditions or curing equipment available or desirable, and even for anadjustment within the relatively narrow range where such adjustmentswere feasible, one had to carefully determine by preliminary tests foreach crosslinking formulation the proper balance between curing time andcuring temperature. Curing at low temperatures such as for instance toC. with curing times below 2 minutes was impossible.

This invention relates to improvements in crosslinking formulationswhich produce better mechanical properties of the crosslinked cellulosefibres at the same or even higher levels of crease recovery or wash andwear performance.

According to the present invention there is provided a method ofintroducing crosslinks to a cellulosic fibre or material, which processcomprises treating the material with a solution containing 1. acrosslinking agent comprising a mixture of an aldehyde having amolecular weight not greater than 60 and a nitrogeneous compound havinga molecular weight of not greater than 250, said nitrogeneous compoundhaving at least two groups, said groups being adjacent a carbonyl group,

the molar ratio of aldehyde to nitrogeneous compound being from about12:1 and about 2:1;

2. a catalytically effective amount of a mixture of (a) i a potentiallyacidic inorganic salt of zinc or magnesium, and (b) a salt offluorine-containing acid selected from the group consisting of alkalimetal, al-

fluorides, and

3. an abrasion resistance improving additive comprising from about 0.03to about 3.0 mols of a neutral alkali metal salt of an inorganicmonobasic acid.

This invention provides a new crosslinking system for fibrous materialat least partly consisting of cellulosic fibres, particularly fibrousmaterial present in the form of textile sheet material such as woven orknitted fabrics.

In some of its embodiments, this invention provides a crosslinkingsystem which is inexpensive, simple to carry out and which requiresapplication of a relatively small amount of solid material to thefibres.

which can be modified in a simple way by means of additives to givepredeterrninable variations of finishing effects and mechanicalproperties, i.e., which can be adapted to requirements simply by varyingthe concentration of additives or finishing effects required and/orlosses of mechanical strength to be tolerated.

which enables crosslinking to be effected at much higher speeds and yetat lower temperatures than have been necessary for conventionalcrosslinking systems.

which involves a low solids content formulation (where migration duringdrying is much less of a hazard) where most reaction components used inthe formulation are low price chemicals; due to the low solids contentit is in many cases unnecessary to afterwash the textile material aftercrosslinking.

kaline earth metal and zinc fiuoborates and silicowhich enables theobtaining of exceptionally good finishing effects at exceptionally lowlosses of abrasion resistance.

The process of this invention may be carried out on textile materialconsisting of or containing cellulose fibres such as cotton, linen,rayon, polynosic, high modulus rayon, and high wet strength rayon. Thefibres may be in the form of textile sheet material such as woven orknitted fabrics.

In the present process, the aldehyde constituent of the crosslinkingagent mixture may comprise such compounds as formaldehyde, glyoxal andacrolein, or compounds capable of producing these aldehydes, such asacetals.

The nitrogeneous compound of the crosslinking agent mixture may have atleast two 1 groups, adjacent with each group a carboxyl group. The molarratio of aldehyde to nitrogeneous compound of the crosslinking agent maybe between about 12:1 and 2:1, preferably between about 6:1 and 2:1.

The nitrogeneous compound preferably is a dior polymethylol derivativeof a cyclic urea, carbamate, uron or triazone. The nitrogen atom of theN-methylol groups preferably does not contain'a hydrogen atom, but issubstituted with an alkyl, alkoxy, methylol, aceto or a halogenatedalkyl group. The nitrogeneous compound is preferably dimethylol ethyleneurea.

The potentially acidic inorganic salt of the crosslinking catalyst maybe an inorganic salt of magnesium or zinc. The preferred salt of thistype is magnesium chloride. The salts of fluorine-containing acids areselected from silicoborates and fluoborates. The preferred salts are thealkali metal, alkaline earth metal and zinc salts. The ratio of themolar concentration of the potentially acidic salt of thefluorine-containing salt of the crosslinking catalyst may be within therange of from about :1 to about :1.

The ratio of the molar concentration of the catalyst mixture to themolar concentration of the crosslinking agent may be from about 1:4 toabout 1:15.

The abrasion improving additive may be a neutral salt selected fromchlorides, bromides, thiocyanates and nitrates of the alkali metalssodium, potassium and lithium. Preferred modifiers are lithium chloride,lithium thiocyanate and sodium thiocyanate.

The treating solution may also include a cure retardant which may be anitrogeneous compound having at least one amino group. The compoundpreferably has the formula in which R, R" and R are alkyl such as methylor ethyl, acyl, oxyalkyl or alkoxy alkyl groups. The nitrogeneous cureretarding agent ordinarily will be present in the treating solution at aconcentration not exceeding about 0.1 mol per litre.

The cure retardant may also comprise an alkali metal thiocyanate. Wherethe agent which improves abrasion resistance is an alkali metalthiocyanate, such compounds also serves as a cure-retarding agent. Wherethe cure-retarding agent is a thiocyanate, it will ordinarily be presentin the treating solution at a concentration of less than about one molper litre.

Other agents such as softeners, hydrophobing or flame-retarding agents,white or colored pigments, or dyestuffs may also be present in the bath.

The solvent for the treating solution may be aqueous or non-aqueous.Typical non-aqueous solvents are chlorinated hydrocarbons. Prior toheating the treated fibres to effect crosslinking, the solvent isremoved, at least partially, by evaporation.

Crosslinking may be effected by heating in a dry state or if desired inpresence of residual moisture (a dry cure being the preferred method),or by applying energy by irradiation. This crosslinking treatment may becarried out in one or in several steps involving if desired differentreaction conditions as to the degree of swelling of the fibre, thetemperature/duration of the cure or to reaction catalysts. The finalcuring step may be carried out after the textile material has beensubjected to conventional textile processing (fibres spun into yarns,processing yarns into fabrics, fabrics into garments).'

The curing conditions used to effect crosslinking according to thepresent invention are such that the abrasion improving additives haveper se virtually no catalytic effect, i.e., they will not produce anyappreciable and durable increase of dry crease recovery if applied tocellulose fibres together with the crosslinking agents in absence of thecatalyst mixture mentioned above and subjected to curing conditionswhich in presence of the catalyst mixture will produce a high degree ofcrosslinking, nor will their presence appreciably affect the degree ofdry crease recovery angles obtained. Their main effect thus is onmechanical properties, in particular on the abrasion resistance asdetermined for instance according to AATCC 934966, a standardized methodfor determining the abrasion resistance, developed by the AmericanAssociation of Textile Chemists and Colorists. The term abrasionimproving additive thus essentially means an agent which when added tothe crosslinking formulation will produce very substantially better wearresistance for a given level of crease recovery. The amount and kind ofreaction modifier added to the formulation is determined by requirementsas to the maximum loss of abrasion strength which can be tolerated at agiven level of crosslinking. The addition of such agents will of courseincrease costs to a small degree, and they thus will be added only tothe degree necessary to obtain beneficial effects on mechanicalproperties. Some of these additives, in particular lithium salts, willimprove wash and wear ratings by raising wet creasing angles virtuallywithout affecting dry crease recovery.

The cure-retarding agents may be used to adjust curing conditions torequirements as regards curing temperatures and curing time. In mostcases the mildest cure (low temperature, short reaction times) will bethe most economical and also the most desirable cure with regard to theprevention of heat induced discoloration and to hydrolytic damage to thecellulose present. In some cases it is, however, desirable to use asystem which requires a hard cure, for instance if the processingsequence commonly called post-cure, Permanent Press or Durable Press isto be used, i.e., where curing is effected only after making-upoperations, or in cases where fabrics are to be embossed or subjected toother treatments involving mechanical deto change the ratio betweenother components of the system or to use different agents.

The treatingsolution of this invention may be applied to textilematerial in the form of single fibres, yarns or woven, knitted ornon-woven fabrics. The preferred application, however, is to apply tothe textile material the components and agents from a bath, to removethe 120C, these temperatures being increased by 10C.

for 5 g/litre, 20 for 10 g/l and 30 for 20 g/l of the triazone or'35C.if 0.5 to 1 mol ofNaCNS was present). The aim of most trials was tocompare mechanical properties (tensile strength loss, abrasionresistance) at the same level of dry crease recovery and/or wash andsolvent, i.e., to dry at least partly and to effect .crosslinking of thecellulose by subjecting toa heattreatment (curing). Drying and curingmaybe effected in one or in separate steps. Between drying (which may beonly partial at that state and may be completed subsequently) and curingone may subject the textile material to treatments involving mechanicaldeformation such as to embossing or pressing in a dry state or inpresence of residual solvent, or to known textile processing operationssuch as spinning fibres into threads or yarns, producing textile sheetmaterial from yarns, or to making-up operations on fabrics. The textilematerial may consistof cellulose fibres alone, or of blends ofcellulosic with non-cellulosic fibres such as for instance syntheticthermoplastic fibres spun from polyamides, polyesters, acrylic orvinylic polymers, polyurethanes, polycarbamates, polyefins, fromcopolymers, from mixtures of polymers of from thermoplastic materialsuch as cellulose esters. The cellulose component may be nativecellulose such as cotton and linen, or regenerated cellulose fibres suchas rayon,. polynosic, high modulus, high wet strength rayon fibres orchemically modified regenerated cellulose fibres.

Following is a description by way. of example .only of methods ofcarrying the invention into effect.

In the following examples, asatisfactory level for noiron, Durable Pressor Permanent Press performance. on an all cotton shirting broadcloth, isconsidered to be a wash and wear rating of 4.5 or higher of AATCC88-1961 T Standard, dry creasing angles of around 300 (sum of warp andfilling) according to AATCC 66-1968 a maximum tensile strength loss ofaround 50 percent and as an acceptable Accelerator abrasion resistance(determined according to AATCC 93- l969),a weight loss of less thanpercent.

These values are widely acceptedas borderlines for Durable Press orNo-Ironall-cotton fabrics all over the world. In the case of blends,these accelerator abrasion and tensile strength loss values do notapply.

In order to obtain-comparable results in the following I examples, allcrosslinking treatments were carried out by the pad-drycure method,i.e., by paddingthe formulation on to the'fab'ric (pick-up 70 to 75percent),

drying to less than 2 percent humidity at temperatures notexceeding.120, followed bycuring at the proper,

temperature DMEU andcarbamate with MgCl at catalyst: 3 minutes at 150C.,with MgCl lfluoborate: 1 minute at 130C., DMEU with MgCl as catalyst 3min-.

utes at 145C with MgCl plus fluoborate 1 minute at wear performance.

All concentrations listed in Tables I to IV are in grams per litre.

Abrasion resistance is in percent weight loss after the standardabrasion test described in AATCC 93l969.

w Table I, belowfdemonstrates that mixtures of an al- A comparison ofExamples 1 and 2 shows that while formaldehyde by itself is a strong andcheap crosslinking agent when used with the fluoborate/mag'nesiumchloride catalyst, a concentration of 27 g/l solid formaldehyde is toolow for obtaining a wash and wear rating of 4.5 even though the tensilestrength loss already is reaching 55 percent and abrasion strength is nolonger acceptable for practically all end uses. An increase oftheformaldehyde concentration to 36 g solid formaldehyde per litre (100g 36 percent solution) as in Example-2, does give a wash and wear-ratingof 4.5, but tensile strength losses and abrasion strength are totallyunacceptable.

In the case of DMEU or carbamate used above, (Examples 3 and 4), thesituation is similar. To obtain good wash and wear ratings, one has toapply high concentrations, which give excessive tensile and particularlycent). These effects are. shown only by the mixtures forming the subjectof the present invention, irrespective of the nitrogeneous compound usedtogether with formaldehyde, (DMEU responding best) as is shown in thefollowing tables. Examples 6 and 7 also show that these formulations arecheap and have a very low solids concentration, thus affecting the handto much lesser degree and showing a much lower tendency for theformation of surface resin due to migration during drying.

- Formaldehyde (36% sol.) DMEU (50% sol.) Q

TABLE I' Fabric: Cotton poplin, bleached and mercerized '100 g 7's g g g80 g TABLE I Fabric: Cotton poplin, bleached and mercerizcd DMPU (50%sol.) Carbamate (N-ethyl.) (50% sol.) 180 g 180 g MgCl o aq. g 20 g 20 g40 g 40 g 20 g 20 g NaBF 2g 2g 2g 2g 2g 2g 2g LiCl 40 g 40 g NaCNS 80 gSoftener 30 g 30 g 30 g 30 g 30 g 30 g 30 g Tensile Strength loss"(lill)55% 75% 37% 61% 58% 43% 47% Abrasion 24.5% 34.4% 12% 24% 21% 6.5% 7.5%Wash & Wear Rating" 4 4.5 2.75 4.5 4.5 4.75 4.5 Dry Crcasing Angle" 300310 275 310 290 310 305 (1) Determined according to ASTM 1) 1682-64. (2)Determined according to AATCC 93-1969. (3) Determined according to AATCC88-1961 T. (4) Determined according to AATCC 66-1968.

Table II, below, demonstrates that mixtures of forlating 4.5 4.5 4.0

ry creasing maldehyde with DMEU in different ratios within the angles,

ranges defined in the specification gives an excellent balance ofproperties.

Table II also shows that there is an optimum concentration for thelithium chloride (Examples 11, 12 and 13).

TABLE ll Fabric: Cotton poplin, bleached and mercerized Formaldehyde(36% sol.) 75 g 50 g 50 g 50 g 50 g 50 g DMEU (50% sol.) 80g 80g 100g100g 100g 100g MgCI -(a aq. 20 g 20g 20 g 20 g 20 g 20 g NaBF. 2g 2g 2g2g 2g 2g LiCl 40 g 40 g 40 g 20 g 40 g 60 g Softener g 30 g 30 g 30 g 30g 30 g Tensile strength (loss fill.) 43% 40% 36% 38% 43% Abrasion(2)6.5% 7.5% 7.1% 5.2% 4% 4.2% Wash and Wear Rating(3) 4.75 4.5 4.5 DryCreasing Angles(4) 300 290 290 290 290 295 Table lll, below, shows thatvarious widely used rii trogeneous cross-linking compounds when used inmixture with formaldehyde give an excellent balance of properties.Example 16 shows that an acetal (a polyethylene glycol acetal in thiscase) can be substituted for formaldehyde in the aldehyde/nitrogeneouscompound mixture to obtain similar results.

Wash and Wear different blends including polynosic and polyester fibreblends. Examples 17 and 18 demonstrate that improved abrasion resistancecan be obtained on blends. The frosting effect observed oncrossdyedcotton polyester blends, which is due to preferentialfibrillation and removal of crosslinked cotton fibres, was found to be 4for the fabric treated according to Example 17 (with LiCl), while it was3 for the same fabric given a conventional treatment, the untreatedmaterial having a rating of 4.5, i.e., only slightly better than thesample treated according to Example 17 (5 is the best rating). Example19 demonstrates that sodium silicofluoride may be used in place of thefluorborate without affecting effects.

Dry creasing angles(4) What is claimed is:

1. A process for crosslinking cellulose fibres which comprises treatingcellulose fibres with a solution containing l a crosslinking agentcomprising a mixture of an aldehyde having a molecular weight notgreater than 60 and a nitrogeneous compound having a molecular weightnot greater than 250, said nitrogeneous compound having at least twogroups, and each such group being adjacent a carbonyl group, the molarratio of aldehyde to nitrogeneous compound being from about 12:1 to 2:1;(2) a catalytically effective amount of a mixture of (a) magnesiumchloride, and (b) a salt of a fluorine-containing acid selected from thegroup consisting of alkali metal, alkaline earth metal, and zincfluoborates and silicofluorides, the molar ratio of magnesium chlorideto that of the salt of, a fluorine-containing acid being in the rangebetween about :1 and 15:1, and the molar concentration of the catalyticmixture to the molar concentration of the crosslinking agent mixture insaid solution being in the range of from about 1:4 to about 1:15, and(3) as an abrasion improving additive from about 0.3 to about 3 mols perlitre of a neutral lithium halide or alkali metal thiocyanate, andheating said fibres to cause said crosslinking agent to react with saidfibres.

2. The process of claim 1 wherein the molar ratio of aldehyde tonitrogeneous compound of the crosslinking agent is between about 6:1 andabout 2:1.

3. The process of claim 1 wherein said nitrogeneous compound is selectedfrom the group consisting of diand poly-methylol derivatives of cyclicureas, carbamates, and triazones.

4. The process according to claim 1 wherein said aldehyde isformaldehyde.

5. The process of claim 3 wherein the nitrogeneous compound isdimethylol-ethylene urea.

6. The process of claim 1 wherein the abrasion improving additive islithium chloride.

7. The process of claim 1 wherein the salt of a fluorine-containing acidis sodium fluoborate.

8. The process of claim 1 wherein the catalyst comprises a mixture ofmagnesium chloride and sodium fluoborate.

9. The process of claim 1 wherein the solution for treating thecellulose fibres is an aqueous solution.

10. The process of claim 1 wherein said treating solution contains fromabout 0.5 to about 1.5 mols per litre of said crosslinking agentmixture.

1 l. The process of claim 10 wherein said treating solution containsfrom about 0.6 to about 1.0 mols per litre of said crosslinking agentmixture.

12. The process of claim 1 wherein said treating solution contains as acure-retarding agent a nitrogeneous compound having formula 14.Cellulosic fibres which have been treated according to the process ofclaim 1.

2. The process of claim 1 wherein the molar ratio of aldehyde tonitrogeneous compound of the crosslinking agent is between about 6:1 andabout 2:1.
 3. The process of claim 1 wherein said nitrogeneous compoundis selected from the group consisting of di- and poly-methylolderivatives of cyclic ureas, carbamates, and triazones.
 4. The processaccording to claim 1 wherein said aldehyde is formaldehyde.
 5. Theprocess of claim 3 wherein the nitrogeneous compound isdimethylol-ethylene urea.
 6. The process of claim 1 wherein the abrasionimproving additive is lithium chloride.
 7. The process of claim 1wherein the salt of a fluorine-containing acid is sodium fluoborate. 8.The process of claim 1 wherein the catalyst comprises a mixture ofmagnesium chloride and sodium fluoborate.
 9. The process of claim 1wherein the solution for treating the cellulose fibres is an aqueoussolution.
 10. The process of claim 1 wherein said treating solutioncontains from about 0.5 to about 1.5 mols per litre of said crosslinkingagent mixture.
 11. The process of claim 10 wherein said treatingsolution contains from about 0.6 to about 1.0 mols per litre of saidcrosslinking agent mixture.
 12. The process of claim 1 wherein saidtreating solution contains as a cure-retarding agent a nitrogeneouscompound having formula
 13. The process of claim 12 wherein thecure-retarding agent is sodium thiocyanate.
 14. Cellulosic fibres whichhave been treated according to the process of claim 1.